Project Summary Background: The emergence of multi-drug resistant pathogenic bacteria represents a serious and growing threat to human lives and national healthcare systems. These supebugs now kill 100,000 s of people each year and are estimated to add $20bn in healthcare costs in the US. In particular, the expansion of Gram-negative strains such as Klebsiella pneumonia, Escherichia coli, Acinetobacterbaumannii and Pseudomonasaeruginosa and the rapidly spreading NDM-1 phenotypes are of grave concern. For many of these Gram-negative infections, colistin (polymyxin E) remains the only option of last resort , where the carbapenems are no longer active, and cases of tigecycline resistance have been reported. Aims & Objectives: We aim to produce new antibiotics, based on colistin, that are active against resistant super-bugs and that have better safety profiles than current last-resort antibiotics. The research will deliver novel drug-candidates targeted at resistant pathogenic bacteria, and will also provide a detailed scientific understanding of the origins and mechanisms of antibiotic-induced kidney toxicity (nephrotoxicity).We will develop a detailed understanding of how colistin works to kill bacteria. In the longer term, the assays developed for profiling of nephrotoxicity will prove valuable in all areas of drug research, thus providing tools for both antibiotic-renal and more general drug-renal toxicity screening. The new colistin derivatives will be active against the serious Gram-negative super superbugs and attack both drug-sensitive and drug-resistant strains of the bacteria. Approach & methods: This program will use aworld first synthetic method for the rapid synthesis of 1,400colistin analogs for an unprecedented systematic investigation of structure-activity and structuretoxicity relationships. These novel compounds will be optimized for activity against drug-resistant Gram-negative bacteria, in particular NDM-1 strains, and then evaluated for mode of action, stability, cell toxicity and nephrotoxicity. They will also be profiled for binding to the bacterial membranes and molecular target (Lipid A). This will lead to in vivo proof-of-principle for drug action and pharmacokinetic studies for the selection of compounds for future pre-clinical evaluation.